Since mankind first began to build free-standing structures to live and work in, there has been a problem in devising roof structures which are water tight and have acceptable insulating qualities. These problems are compounded even further by the need for making the roof structures reasonable in cost. This is particularly true for large area roof structures such as these commonly found on commercial buildings such as shopping centers, warehouses and the like.
To meet the increasing need for large area roof structures which are water tight and have acceptable insulating and fire resistant qualities, lightweight insulating concrete decks have been resorted to. Traditionally, support beams have been erected with structural concrete forming such as corrugated sheet metal laid thereover. The lightweight concrete is then pumped with a water mixture to the desired thickness and, after properly setting, a waterproof coat is added to the exterior surface. Literally thousands of buildings, shopping centers, gymnasiums, and the like have roofs of this type. After the waterproofing exterior top surface is applied, then the excess free pumping moisture must dry or vent as vapor downward over a period of months to achieve improved insulation qualities and prevent deterioration. Corrugated metal forms without vent or weep holes retain considerable moisture for years, even when roof top vents are used. In those structures where harmful moisture does eventually vent out, moisture from cracks or other openings in the exterior surface, from normal condensation between the corrugated and waterproofed layers, together with retained portions of initial placement water, or by other means accumulates in the roof, thus reducing its insulating capacity and eventually causing deterioration of the entire roof structure.
The above moisture has become such a widespread problem that in new construction weep holes are provided in the corrugated layer in an effort to allow initial placement water trapped moisture to escape. The holes must either be extremely small so that the lightweight concrete poured thereover will not run through the openings or the same must be covered with a liquid impervious material to prevent running.
As to pre-existing roof structures built prior to the availability of corrugations with weep holes, the only alternatives have been to either remove the waterproof exterior layer, allow the concrete surface to dry out, and reseal the same, or, in the alternative, replace the entire roof structure. Neither of these two alternatives are desirable and quite often trapped moisture is allowed to remain further and accumulate in a roof to the point that almost all insulating capabilities are lost and rapid deterioration takes place.